Software Development for a Three-Dimensional Gravity Inversion and Application to Study of the Border Ranges Fault System, South-Central Alaska

The Border Ranges Fault System (BRFS) bounds the Cook Inlet and Susitna Basins, an important petroleum province within south-central Alaska. A primary goal in the research is to test several plausible models of structure along the Border Ranges Fault System using a novel three-dimensional inversion utilizing gravity and magnetic data, constrained with other geophysical, borehole and surface geological information. This research involves the development of inversion modeling software using a Borland C++ compiler as part of the Rapid Application Development (RAD) Studio. The novel inversion approach directly models known geology, and a priori uncertainties on the geologic model to allow researchers to compare alternative interpretations. This technique to evaluate three-dimensional structure in regions of extremely complex and poorly known geology can be applied in other studies of energy resources. The software reads an ASCII text file containing the latitude, longitude, elevation, and Free Air anomalies of each gravity station as well as known gridded surface files of known topography and subsurface units. The contributions of each node in the grid are computed in order to compare the theoretical gravity calculations from a forward model to the gravity observations. The computation of solutions to the linearized inversion yields a range of plausible densities. The user will have the option of varying the body proportions or densities to observe changes in gravity